The biggest procurement process in the NHS is a "dangerous experiment", a union has warned.

Putting cancer and end-of-life services in Staffordshire and Stoke-on-Trent out to tender could potentially hand over decision-making about these aspects of care to private companies, Unison said.

Four local health authorities in the region have begun the procurement process to appoint a "prime provider" for cancer services, and a similar process to search for an end-of-life care provider will begin later this month.

Reports suggest that private health firms are among those poised to bid for the services.

The contracts to provide these services are more than £1.2 billion, reports suggest.

With the 10-year contract to provide cancer care reportedly worth £689 million and the separate contract to provide end-of-life care worth £535 million.

The Guardian newspaper said that Virgin, Care UK, Ramsay Health and other private firms had attended briefings run by Macmillan Cancer Support, which is advising on the process.

But a spokeswoman for Stafford and Surrounds Clinical Commissioning Group (CCG) said that because of procurement regulations she could not say which firms had expressed interest in the running of the services.

The CCG has clubbed together with three other CCGs - Cannock Chase, North Staffordshire and Stoke-on-Trent - to "transform" cancer care in the region.

The aim of the change to services is to ensure that care is " integrated, co-ordinated and personalised around people's needs", according to the programme's website.

Christina McAnea, head of health at the union Unison, said: "This is by far the biggest procurement process in the NHS and is a dangerous experiment.

"We are talking about £1 billion of taxpayers' money and contracts lasting 10 years in vital cancer services and end-of-life care.

"Clinical Commissioning Groups are potentially handing over all decision-making on cancer and end-of-life care to private companies.

"This is much bigger than just asking private companies to provide a service, this is asking them to design the whole system.

"With profit as the main driving force, how can it not lead to problems?"

Labour's shadow health secretary Andy Burnham added: " David Cameron and his ministers need to be reminded that they have never been given the permission of the public to put the NHS up for sale.

"Piece by piece, they are unpicking the NHS and selling it off to their friends in private health.

"That is why Labour has presented a Bill in the House of Commons to repeal the Government's NHS privatisation legislation.

"We will stop the sell-off and restore the right values to the NHS.

"Cameron has placed the NHS on a fast-track to fragmentation and privatisation and the next election is the last chance to change course."

Andrew Donald, accountable Officer for Cannock Chase and Stafford and Surrounds CCGs, said: " Rather than have several organisations each commissioning individual services on individual contracts, we are bringing this all together and plan to appoint one lead organisation or consortia to be the prime provider responsible for co-ordinating cancer care in new ways, to improve outcomes and meet patients' expectations.

"This is the start of an exciting journey that will take 10 years to complete and will make cancer care in Staffordshire and Stoke-on-Trent among the best in Europe."

A Department of Health spokeswoman added: "The key thing is that patients get the best possible care, free at the point of use, no matter who provides it.

"NHS competition rules haven't changed under this Government but the bureaucracy-busting reforms are saving over £1 billion a year."